class Metamodel::ParametricRoleHOW
    does Metamodel::Naming
    does Metamodel::Documenting
    does Metamodel::Versioning
    does Metamodel::MethodContainer
    does Metamodel::PrivateMethodContainer
    does Metamodel::MultiMethodContainer
    does Metamodel::AttributeContainer
    does Metamodel::RoleContainer
    does Metamodel::MultipleInheritance
    does Metamodel::Stashing
    does Metamodel::TypePretense
    does Metamodel::RolePunning
    does Metamodel::ArrayType {}

Warning: this class is part of the Rakudo implementation, and is not a part of the language specification.

A Metamodel::ParametricRoleHOW represents a non-instantiated, possibly parameterized, role:

(role Zape[::T] {}).HOW.say;# OUTPUT: «Perl6::Metamodel::ParametricRoleHOW.new␤» 
(role Zape {}).HOW.say; # OUTPUT: «Perl6::Metamodel::ParametricRoleHOW.new␤» 

As usual, .new_type will create a new object of this class.

my \zipi := Metamodel::ParametricRoleHOW.new_type( name => "zape", group => "Zape");
say zipi.HOW; # OUTPUT: «Perl6::Metamodel::ParametricRoleHOW.new␤» 

The extra group argument will need to be used to integrate it in a parametric role group, which will need to be defined in advance.

Note: As most of the Metamodel classes, this one is here mainly for illustration purposes and it's not intended for the final user to instantiate, unless their intention is really to create a parametric role group.

Type Graph §

Routines supplied by role Metamodel::Naming §

Metamodel::ParametricRoleHOW does role Metamodel::Naming, which provides the following routines:

(Metamodel::Naming) method name §

method name($type)

Returns the name of the metaobject, if any.

say 42.^name;       # OUTPUT: «Int␤»

(Metamodel::Naming) method set_name §

method set_name($type, $new_name)

Sets the new name of the metaobject.

Routines supplied by role Metamodel::Documenting §

Metamodel::ParametricRoleHOW does role Metamodel::Documenting, which provides the following routines:

(Metamodel::Documenting) method set_why §

method set_why($why)

Sets the documentation for a type to $why.

(Metamodel::Documenting) method WHY §

method WHY()

Returns the documentation for a type.

Routines supplied by role Metamodel::Versioning §

Metamodel::ParametricRoleHOW does role Metamodel::Versioning, which provides the following routines:

(Metamodel::Versioning) method ver §

method ver($obj)

Returns the version of the metaobject, if any, otherwise returns Mu.

(Metamodel::Versioning) method auth §

method auth($obj)

Returns the author of the metaobject, if any, otherwise returns an empty string.

(Metamodel::Versioning) method api §

method api($obj)

Returns the API of the metaobject, if any, otherwise returns an empty string.

(Metamodel::Versioning) method set_ver §

method set_ver($obj, $ver)

Sets the version of the metaobject.

(Metamodel::Versioning) method set_auth §

method set_auth($obj, $auth)

Sets the author of the metaobject.

(Metamodel::Versioning) method set_api §

method set_api($obj, $api)

Sets the API of the metaobject.

Routines supplied by role Metamodel::MethodContainer §

Metamodel::ParametricRoleHOW does role Metamodel::MethodContainer, which provides the following routines:

(Metamodel::MethodContainer) method add_method §

method add_method($obj, $name, $code)

Adds a method to the metaclass, to be called with name $name. This should only be done before a type is composed.

(Metamodel::MethodContainer) method methods §

method methods($obj, :$all, :$local)

Returns a list of public methods available on the class (which includes methods from superclasses and roles). By default this stops at the classes Cool, Any or Mu; to really get all methods, use the :all adverb. If :local is set, only methods declared directly in the class are returned.

class A {
    method x() { };
}
 
say A.^methods();                   # x 
say A.^methods(:all);               # x infinite defined ...

The returned list contains objects of type Method, which you can use to introspect their signatures and call them.

Some introspection method-look-alikes like WHAT will not show up, although they are present in any Raku object. They are handled at the grammar level and will likely remain so for bootstrap reasons.

(Metamodel::MethodContainer) method method_table §

method method_table($obj --> Hash:D)

Returns a hash where the keys are method names, and the values are methods. Note that the keys are the names by which the methods can be called, not necessarily the names by which the methods know themselves.

(Metamodel::MethodContainer) method lookup §

method lookup($obj, $name --> Method)

Returns the first matching method object of the provided $name or (Mu) if no method object was found. The search for a matching method object is done by following the mro of $obj. Note that lookup is supposed to be used for introspection, if you're after something which can be invoked you probably want to use find_method instead.

say 2.5.^lookup("sqrt").raku;      # OUTPUT: «method sqrt (Rat $: *%_) ...␤» 
say Str.^lookup("BUILD").raku;     # OUTPUT: «submethod BUILD (Str $: :$value = "", *%_ --> Nil) ...␤» 
say Int.^lookup("does-not-exist"); # OUTPUT: «(Mu)␤»

The difference between find_method and lookup are that find_method will use a default candidate for parametric roles, whereas lookup throws an exception in this case, and that find_method honors FALLBACK methods, which lookup does not.

Routines supplied by role Metamodel::PrivateMethodContainer §

Metamodel::ParametricRoleHOW does role Metamodel::PrivateMethodContainer, which provides the following routines:

(Metamodel::PrivateMethodContainer) method add_private_method §

method add_private_method($obj, $name, $code)

Adds a private method $code with name $name.

(Metamodel::PrivateMethodContainer) method private_method_table §

method private_method_table($obj)

Returns a hash of name => &method_object

(Metamodel::PrivateMethodContainer) method private_methods §

method private_methods($obj)

Returns a list of private method names.

(Metamodel::PrivateMethodContainer) method private_method_names §

method private_method_names($obj)

Alias to private_methods.

(Metamodel::PrivateMethodContainer) method find_private_method §

method find_private_method($obj, $name)

Locates a private method. Otherwise, returns Mu if it doesn't exist.

Routines supplied by role Metamodel::AttributeContainer §

Metamodel::ParametricRoleHOW does role Metamodel::AttributeContainer, which provides the following routines:

(Metamodel::AttributeContainer) method add_attribute §

method add_attribute($obj, $attribute)

Adds an attribute. $attribute must be an object that supports the methods name, type and package, which are called without arguments. It can for example be of type Attribute.

(Metamodel::AttributeContainer) method attributes §

method attributes($obj)

Returns a list of attributes. For most Raku types, these will be objects of type Attribute.

(Metamodel::AttributeContainer) method set_rw §

method set_rw($obj)

Marks a type whose attributes default to having a write accessor. For example in

class Point is rw {
    has $.x;
    has $.y;
}

The is rw trait on the class calls the set_rw method on the metaclass, making all the attributes implicitly writable, so that you can write;

my $p = Point.new(x => 1, y => 2);
$p.x = 42;

(Metamodel::AttributeContainer) method rw §

method rw($obj)

Returns a true value if method set_rw has been called on this object, that is, if new public attributes are writable by default.

Routines supplied by role Metamodel::RoleContainer §

Metamodel::ParametricRoleHOW does role Metamodel::RoleContainer, which provides the following routines:

(Metamodel::RoleContainer) method add_role §

method add_role($obj, Mu $role)

Adds the $role to the list of roles to be composed.

(Metamodel::RoleContainer) method roles_to_compose §

method roles_to_compose($obj --> List:D)

returns a list of roles added with add_role, which are to be composed at type composition time.

Routines supplied by role Metamodel::MultipleInheritance §

Metamodel::ParametricRoleHOW does role Metamodel::MultipleInheritance, which provides the following routines:

(Metamodel::MultipleInheritance) method add_parent §

method add_parent($obj, $parent, :$hides)

Adds $parent as a parent type. If $hides is set to a true value, the parent type is added as a hidden parent.

$parent must be a fully composed typed. Otherwise an exception of type X::Inheritance::NotComposed is thrown.

(Metamodel::MultipleInheritance) method parents §

method parents($obj, :$all, :$tree)

Returns the list of parent classes. By default it stops at Cool, Any or Mu, which you can suppress by supplying the :all adverb. With :tree, a nested list is returned.

class D { };
class C1 is D { };
class C2 is D { };
class B is C1 is C2 { };
class A is B { };
 
say A.^parents(:all).raku;
# OUTPUT: «(B, C1, C2, D, Any, Mu)␤» 
say A.^parents(:all, :tree).raku;
# OUTPUT: «[B, ([C1, [D, [Any, [Mu]]]], [C2, [D, [Any, [Mu]]]])]␤»

(Metamodel::MultipleInheritance) method hides §

method hides($obj)

Returns a list of all hidden parent classes.

(Metamodel::MultipleInheritance) method hidden §

method hidden($obj)

Returns a true value if (and only if) the class is marked with the trait is hidden.

(Metamodel::MultipleInheritance) method set_hidden §

method set_hidden($obj)

Marks the type as hidden.

Routines supplied by role Metamodel::Stashing §

Metamodel::ParametricRoleHOW does role Metamodel::Stashing, which provides the following routines:

(Metamodel::Stashing) method add_stash §

method add_stash($type_obj)

Creates and sets a stash for a type, returning $type_obj.

This method is typically called as the last step of creating a new type. For example, this is how it would be used in a minimal HOW that only supports naming and stashing:

class WithStashHOW
    does Metamodel::Naming
    does Metamodel::Stashing
{
    method new_type(WithStashHOW:_: Str:D :$name! --> Mu) {
        my WithStashHOW:D $meta := self.new;
        my Mu             $type := Metamodel::Primitives.create_type: $meta, 'Uninstantiable';
        $meta.set_name: $type, $name;
        self.add_stash: $type
    }
}
 
my Mu constant WithStash = WithStashHOW.new_type: :name<WithStash>;
say WithStash.WHO; # OUTPUT: «WithStash␤»